Electrical issues leaving me stumped on my 04

[TylerHagerdorn]

This 04 is driving me crazy trying to figure these electrical gremlins out. The indicator light on the AWD switch constantly flickers and or goes out when I push the brake pedal. Sometimes when I turn the truck off and take the key out it'll beep once or twice like I'm locking the truck. Sometimes the rear wiper will work when I turn the switch and sometimes it won't do a thing. Do I have a bad ground somewhere or could that be the BCM going bad? Also when I park it the fuel range will go down and down and then it'll go back up while you sit. It doesn't do it while driving. And the oil pressure gauge likes to sit between 20 and 40 at idle, where my 01 Yukon always sat at 40-50 no matter what. And also if I have the 40 amp j case ABS fuse installed the abs light will go out and then if I try to accelerate it makes this horrible noise under the dash but if I remove it it's fine. I've checked the wiring I can see and it all looks fine. If anyone has any advice that would be great.

 

[MassHoe04]

Ground connections would be a good place to start. A bad ground can make current fluctuate, which electronic control modules and computers do not like.

Check and clean. Maybe it will fix all or some of your gremlins.
If nothing else, you'll be able to eliminate bad grounds as a possible cause.

 

[TylerHagerdorn]

Ground connections would be a good place to start. A bad ground can make current fluctuate, which electronic control modules and computers do not like.

Check and clean. Maybe it will fix all or some of your gremlins.
If nothing else, you'll be able to eliminate bad grounds as a possible cause.

I've replaced almost every ground I can find. Replaced all the ones under the hood except the one going from the battery to the front frame. Also replaced the ones under the drivers door at the frame. If there are some I'm missing let me know please.

 

[MassHoe04]

You don't always have to replace everything... depends on condition.

You do want to be sure grounds are good.
Controls and computer boards start doing really weird things when they see even a slight reduction of the power they need or have brief interruptions (even nanoseconds) in the power.

The main ground from the battery to the back of the engine block is a critical item for the whole system.
I should be cleaned of any rust or corrosion, tight and making solid metal to metal contact.

The negative cable on my Jeep looked fine, but was actually corroding inside the rubber insulation after twenty years of water finding its way inside the jacket. It started impacting the cable's ability to fully ground the system to the engine block and chassis.

No ground, you get nothing.

Having poor or intermittent grounds, often makes things work sometimes and not work other times.
Also, poor or intermittent grounds can make things act strange sometimes; and drive you crazy all the time...

At this point you just want to do what you can to see if grounding issues can be completely ruled out as the cause for your troubles. Or, possibly fix them in the process.

 

[TylerHagerdorn]

I replaced the grounds because they were broken or corroded. There isnt one from the battery to the block. There is one from the pcm to the block and one from the block to a stud on the firewall. The one from the battery goes to the front frame/crossmember.

 

[Fless]

SWAG: pull both PCM connectors off and inspect both the connector side and the PCM side for water intrusion, especially in the lower pins. The PCM connector gaskets do have a tendency to leak and can be replaced.

 

[rockola1971]

Grounds and have the battery load tested and make sure the alternator is not producing a substantial amount of AC leakage current because of rectifiers (diodes) going bad in the alternator.
Im curious about this "AWD switch". Whats that all about?

 

[TylerHagerdorn]

Grounds and have the battery load tested and make sure the alternator is not producing a substantial amount of AC leakage current because of rectifiers (diodes) going bad in the alternator.
Im curious about this "AWD switch". Whats that all about?

The alternator is new. It's an ac Delco. I replaced it because whoever owned the truck before me put the 105a alternator in the truck when the RPO code called for the 140/145a alternator. I don't know how long it was on the truck either before I swapped it. There's nothing wrong with the alternator. Battery tested fine. The truck has the optional all wheel drive, not 4wd. The switch im talking about is where the selectable 4wd switch is. My truck has AWD with selectable 4 wheel low. The switch to the left of the gauges.

 

[TylerHagerdorn]

SWAG: pull both PCM connectors off and inspect both the connector side and the PCM side for water intrusion, especially in the lower pins. The PCM connector gaskets do have a tendency to leak and can be replaced.

Ive already done that. There is no water intrusion everything was good and sealed. Didn't see any corrosion or evidence of water getting in it.

 

[o4TahoePE]

I had the same exact problem with my 04 Tahoe. Drove me crazy for about 2 years. It turned out to be a ground cable that was supposed to be attached to the drivers side frame just above the front suspension. When I had the front end rebuild I guess the shop I had do it failed to re-attach the ground cable. After re-attaching the cable everything was back to normal with no problems at all. Let me know if you would like me to take a picture of it so you can see what it is.